With a mathematical model, they explained why the genomes of living beings preserve “junk DNA”

He human genome It is made up of three billion base pairs. Only 2% code proteins. The remaining 98% were considered with less important functions, but this view has started to change.

They call it the “unwanted DNA“, and now researchers from Tel Aviv University, Israelprovided vital data on why it persists non-coding DNA. The results could help to better understand the rich variety of genome sizes of living beings.

The study, which was funded by the Israel Science Foundation, was published in the journal Open biology. The presence of “junk DNA” in chromosomes was first detected in the 1960s.

In 1977, two scientists named Richard Roberts and Phillip Sharp separately observed that much of this DNA disorder was not only scattered among the genes, but often interrupted them in the middle of the sequence, a discovery which later earned them the Nobel Prize.

Known as introns, they appeared to burden complex cells such as those of humans, while leaving simpler ones, such as those of bacteria, unaffected. Moreover, they added a lot of work to the “transduction process” of DNA into something material.

Each time a protein was created, these breaks in the genetic matrix had to be removed. This required reconstructing the coding instructions before interpreting them as a protein. A daily comparison would be having to weed out thousands of nonsense words just to read one sentence.

This seemingly useless mode of operation is necessary throughout nature, lucky bacteria and other prokaryotes being the exceptions.

The number of introns also differs greatly between species: humans have nearly 140,000 introns, rats about 33,000, fruit flies nearly 38,000, yeast (Saccharomyces cerevisiae) only 286 and the unicellular fungus Encephalitozoon tunnels only 15.

A pending question is Why was unwanted DNA left in organisms? “Interestingly, the reverse has supposedly been the case, as eukaryotes have larger genomes, longer proteins, and much larger intergenic regions than prokaryotes,” the scientists wrote in the Israeli study on introns.

The researchers proposed that deleting any intronic DNA fragments around the coding regions would likely harm the animal’s survival, since the coding sections could also be deleted at the same time.

“Deletions that occur near edges sometimes protrude into the conserved region and are therefore subject to strong purifying selection,” the researchers said.

This “border-induced selection”, in which a neutral sequence is placed between the coding regions, would therefore create an insertion bias for short non-coding DNA sequences.

Essentially, “junk DNA” acts as a mutational buffer: it protects regions that contain the most sensitive sequences needed to code for proteins. To demonstrate this dynamic in action, the researchers created a mathematical model.

It had previously been suggested that “deletion bias leads to shrinkage of genomes during evolution,” the team explained. “The counterintuitive finding that long evolutionarily neutral sequences can arise even under strong deletion bias is due to the rejection of deletions that encroach on the highly conserved edges of neutral sequences.”

Although his model offers a plausible explanation for the variation in intron length within a species, it cannot explain why introns differ between species.

“A trivial explanation is that the model parameters themselves evolve,” the scientists said. “Thus, different species have different insertion-deletion ratios and possibly different propensities for the appearance of conserved regions in introns.”

Knowing there is a bias might help explain the variety of introns what we see in nature and why some organisms seem more genetically “chaotic” than others. The origin of these disturbances is also investigated, with a long history of outdated viruses and genes as sources.

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